The invention is based on an electrical component with fault arc protection, as claimed in the precharacterizing clause of patent claim 1. This component has an insulator in the form of a pillar, to whose head a first electrical conductor system is attached which can be connected to a first electrical potential, in particular a high-voltage potential. A second electrical conductor system is attached to the insulator foot, and can be connected to a second electrical potential, in particular ground potential. The first and the second electrical conductor systems each have an arcing electrode, which arcing electrodes each themselves contain one of two electrode sections which have an annular shape and which are separated from one another in the direction of the pillar axis and are separated from the insulator in the radial direction. Any fault arc which is formed in the event of an undesirable discharge between the two electrical conductor systems is commutated onto the annular electrode sections. The influence of the magnetic field of the current flowing in the annular electrode sections now causes the predominantly axially aligned fault arc to rotate and then to be quenched, for example at the current zero crossing.
The precharacterizing clause of the invention refers to a prior art for electrical components with fault arc protection as is described in U.S. Pat. No. 5,903,427 A. An electrical component with fault arc protection as described in this patent publication contains two electrical conductor systems which are held by an outdoor insulator, in the form of a pillar, such that they are electrically isolated from one another, and which are at different electrical potentials. Each of these systems contains its own conductor section, which is in the form of an open, annular loop and is routed around the insulator in the region of the insulator head or insulator foot, respectively, with a gap. If an undesirable fault arc occurs on the component during operation of the component in a high-voltage systemxe2x80x94for example due to a lightning strike or due to a switching processxe2x80x94then the fault arc is guided into a current path which contains the conductor sections as arcing electrodes. The fault arc is now aligned predominantly axially and has its base on the two annular arcing electrodes, which are in the circumferential direction. The electromagnetic forces cause the fault arc, which is based on the arcing electrodes, to rotate about the insulator of the component until it is quenched, for example at the zero crossing of the fault arc current. The component is thus protected against the eroding and corroding effect of the fault arc.
A further electrical component with fault arc protection and which is in the form of a surge arrestor is specified in U.S. Pat. No. 6,018,453 A. In this component as well, undesirable fault arcs are commutated onto two arcing electrodes, which are spaced apart from one another in the direction of one axis of the component, in order to be forced to rotate about that axis and thus to be quenched, for example at the zero crossing. However, in contrast to the abovementioned prior art, the two arcing electrodes in the case of this component are each in the form of a plate, and a large number of predominantly radial slots are integrally formed in each of the plates.
The invention, as it is defined in the patent claims, achieves the object of specifying an electrical component with fault arc protection of the type mentioned initially, in which the eroding and corroding effect of undesirable fault arcs is, in particular, suppressed particularly effectively.
In the component according to the invention, at least one of the two arcing electrodes is in the form of a cup and has a cup base, which is attached to one electrical connection of the component, as well as a cup wall, which is adjacent to the cup base and extends predominantly in the direction of the axis of the insulator, and in which at least two material recesses are formed which extend from the cup base to the cup rim and are predominantly in the circumferential direction. Designing the arcing electrode in the form of a cup makes it easier for a fault arc, which is formed during operation of the electrical component according to the invention in a high-voltage system, to move outward from its point of origin on the component to the rim of the cup. Since, in the cup wall, the arcing current flows in a number of electrical conductor elements which are predominantly in the circumferential direction with some of them being arranged axially one above the other in the form of a coil, and which are bounded by material recesses, a strong, predominantly radially directed, magnetic field is formed at the base point of the fault arc. An electrodynamic force which is directed at right angles to the magnetic field and at right angles to the arc axis, and which causes the arc to rotate rapidly, as desired, about the axis of the component, now acts on the fault arc, which is predominantly in the axial direction. The fault arc can thus very quickly be moved away from those regions of the component according to the invention which are at risk of arcing erosion and arcing corrosion, virtually independently of the intensity and position of the fault arc, and can be quenched.
The design of the arcing electrode as a cup is of major importance to the stabilization of the fault arc, since the arcing base point is fixed in the axial and radial directions on the cup rim, and can now move in the desired manner in the circumferential direction. In order to keep the material erosion on the arcing electrode as small as possible, it is recommended that the cup rim be formed from fire-resistant material.
A particularly effective embodiment of the cup wall as a coil, and hence particularly rapid rotation of the fault arc, are achieved if at least one of the two material recesses is in the form of a slot and has two sections of different width. In this case, a section which is adjacent to the cup base and has a large slot width is in the circumferential direction while, in contrast, a second section which is adjacent to this section and has a small slot width is predominantly in the circumferential direction and in the axial direction.
Sufficiently good protection against fault arcs is in general achieved if the cup wall is arranged inclined through an angle of more than 10xc2x0 but less than 90xc2x0 with respect to the cup base. The protection is optimized with an inclination angle of 30xc2x0 to 60xc2x0, preferably approximately 45xc2x0.
For sufficiently good arc protection for the component according to the invention, it is important that the height of the arcing electrode, which extends in the direction of the pillar axis, is at least 0.1 and at most 0.5 times its diameter. Such a shape can be achieved by casting or by forming, for example crimping, of a round circular plate which contains preformed material recesses and has a wall thickness of between 2 and 25 mm.
In general, in the component according to the invention, the insulator is hollow and an active part, which is guided axially by the insulator, is provided. Particularly preferred components are an outdoor bushing and a surge arrestor, in particular with an active part based on metal oxide.